This invention relates to the production and heat treating of titanium alloys, and, more particularly, to the preparation and heat treatment of alloys of the gamma titanium aluminide type.
Titanium aluminides are a class of alloys whose compositions include at least titanium and aluminum, and typically some additional alloying elements such as chromium, niobium, vanadium, tantalum, manganese, or boron. The gamma titanium aluminides are based on the gamma phase found at nearly the equiatomic composition, with roughly 50 atomic percent each of titanium and aluminum, or slightly reduced amounts to permit the use of other alloying elements. The titanium aluminides, and particularly the gamma titanium aluminides, have the advantages of low density, good low and intermediate temperature strength and cyclic deformation resistance, and good environmental resistance.
Gamma titanium aluminides can be used in aircraft engines. They potentially have applications such as low-pressure turbine blades and vanes, bearing supports, compressor casings, high pressure and low pressure hangers, frames, and low pressure turbine brush seal supports.
One area of continuing concern in the titanium aluminides, and particularly the gamma titanium aluminides, is their low-to-moderate levels of ductility. Ductility is the measure of how much a material can elongate before it fails, and is linked to other properties such as fracture resistance. The gamma titanium aluminides typically elongate only 1-4 percent at most prior to failure, and have a steeply rising stress-strain curve. Maintaining the strength and resistance of the material to premature failure is therefore highly dependent upon controlling the alloy ductility. Additionally, it is important to maintain good resistance of the material to creep deformation at elevated temperatures.
There is a need for an approach to achieve good mechanical properties in gamma titanium aluminide alloys, and in particular in cast articles which cannot be thermomechanically processed. The approach must permit those properties to be achieved consistently and controllably in the alloys of interest. The present invention fulfills this need, and further provides related advantages.